Generally, electronic cigarettes emit vapor to cater users by utilizing atomizers to heat and atomize e-liquid. As people's awareness of health increasing, the harm of tobacco is generally recognized thus electronic cigarettes become widely used instead of traditional cigarettes gradually.
When e-liquid is used up, electronic cigarettes of the prior art proceed to work only when the liquid storage device is replaced or replenished with e-liquid manually. Moreover, if a user keeps using the electronic cigarette in which e-liquid is nearly used up without adding e-liquid or replacing the liquid storage device, the electronic cigarette would be burn out and scrapped, and worse than that, when e-liquid is used up or insufficient, the heating unit tends to dry burn and produces pernicious gas and burnt matter which would be inhaled by the user and causes health problems. Referring to FIGS. 1-2, a table and a curve graph both show the comparison of the surface temperature change of the heating coil over time in normal status and in e-liquid shortage status. It can be seen from the figures that when e-liquid is used up, the surface temperature of the heating coil rises fiercely, which easily leads to burnout of the electronic cigarette and harm to user's health.